is the basement flooding because of the sump pump being overwhelmed or by the sewer backing up?

or is it seeping from where the floor and the walls meet?

has anyone found any solutions to basement flooding? with the torrential rains, the sump pump could not keep the basement dry and then sewage came in from the street, even with a backflow preventer.

the incompetent jcmua keeps saying they don't have the money to replace the existing combined sewer.